Known methods for extracting collagen include extracting collagen from calf hide by grinding the hide, rinsing the ground hide with a solution of sodium bicarbonate and water, centrifuging and dissolving the recovered solid in water at a pH of 3.0. The resulting collagen solution is then treated with pepsin for 5 to 10 days to remove the telopeptides (non-helical end portions) from the tropocollagen to produce atelocollagen ("soluble" collagen lacking telopeptide). The atelocollagen solution is then filtered through a 0.65 .mu. MILLIPORE filter, is re-precipitated by raising the solution pH and the precipitate is then separated by centrifugation and then lyophilized to dry. The dried collagen is then dissolved in distilled water by acidification with 0.1 M HCl to a pH of 3.0. An ethylenically unsaturated compound and a cross linking agent are added thereto and the resulting mixture is placed in disposable plastic syringes, degassed, centrifuged to remove bubbles and then poured into contact lens molds under a nitrogen atmosphere. The mixture is then exposed to gamma-irradiation. The resulting lenses are neutralized in BOIL 'N SOAK.TM., Burton, Parsons & Co., Inc., according to U.S. Pat. No.: Re. 33,997 to Kuzma et al.
Kuzma's method is problematic in that it results in weak atelocollagen-based hydrogels that do not allow the production of permanent intraocular lenses that can be implanted into the eye. The present invention provides a strong, collagen based hydrogel suitable for producing permanent intraocular lenses for implantation into the eye of a patient.